1. Field of Invention
The present invention relates to an amplifier circuit, and more particularly to a front-end equalizer and amplifier circuit.
2. Description of Related Arts
Front-end equalizer and amplifier circuits are widely used in the integrated circuits and systems, and especially in a high-speed channel receiver for compensating for the loss of spectral component on the transmission medium while high-speed signal transmission.
In the traditional technology, the circuit is constructed by cascading multi-stage fully differential amplifiers. Increase of series causes some difficulties in the matching circuit, the noise in the multi-stage cascade system is also progressively accumulated, and simultaneously, the multi-stage cascade system increases the phase distortion, such that the jitter of the transmission signal is increased. As shown in FIG. 1, the main mismatch influence caused by the cascade structure is described as below.the voltage influence caused by the mismatch: VOSC(total)=A2×A3×Vosc1+A3×Vosc2+Vosc3
Therefore, the influence of the first-stage mismatch voltage is amplified and becomes the largest owing to the latter two amplifiers, and is A2×A3 times that of the single-stage system.
The main influence caused by the noise is described as below.Vnoise(total)=A2×A3×Vnoise1+A3×Vnoise2+Vnoise3
Here, A2 denotes the gain of the first-stage amplifier, A3 denotes the gain of the second-stage amplifier, Vnoise1 denotes the output noise of the first-stage amplifier, Vnoise2 denotes the output noise of the second-stage amplifier, and Vnoise3 denotes the output noise of the third-stage amplifier.
Owing to the latter two amplifiers, the influence of the first-stage mismatch voltage is amplified and becomes the largest, and is A2×A3 times that of the single-stage system. At the receiving end of the high-speed channel, the phase is distorted owing to the effect of the large mismatch and the noise accumulation. Accordingly, the jitter of the transmission signal is increased.